The present invention is related to a method and apparatus for maintaining a state of charge (SOC) for electric batteries in a parallel hybrid electric vehicle (PHEV).
Passenger comfort and fuel efficiency have set forth increasing demands on automotive vehicle designs. It is a primary goal of most vehicle designs to provide a more efficient vehicle without having to sacrifice passenger comfort and satisfaction.
Moreover, and as alternative vehicle propulsion systems are implemented, passenger comfort and fuel efficiency are sometimes in opposition to each other. This is particularly true in hybrid vehicle designs.
A Hybrid Vehicle is a vehicle that has two sources of propulsion. A hybrid electric vehicle (HEV) is a vehicle wherein one of the sources of propulsion is electric and the other source of propulsion may be derived from fuel cells or an internal combustion engine (ICE) that burns diesel, gasoline or any other source of fuel.
Generally, a hybrid vehicle utilizes either one or two drive trains wherein the internal combustion engine (ICE) provides torque to one of the drive trains and an electrical driving force is applied to either of both of the drive trains.
In addition and in order to provide a secondary source of power, hybrid vehicles also utilize a concept known as regenerative braking. Generally, regenerative braking is the conversion of the vehicle""s kinetic energy into a source of electrical power. The vehicle""s kinetic energy is converted from the spinning wheels, in response to a user request to slow or stop the vehicle. A generator is manipulated, and accordingly, produces electrical energy as it applies a stopping force to the vehicle""s axle and/or drive train in response to a stopping request. Therefore, and in accordance with regenerative braking, the kinetic energy is converted to electric energy, as the vehicle begins to slow down.
In order to operate the internal combustion engine (ICE) of a hybrid vehicle a fuel source must be consumed. This causes the engine to generate emissions that are harmful to the environment and the reduction of such emissions is a primary goal of any hybrid vehicle design. On the other hand, an electric drive system produces little or no emissions, however, the operation of such a system draws energy from a battery or plurality of batteries which ultimately must be recharged.
Accordingly, and in order to operate in a most efficient manner, either one or both of the energy sources of a hybrid vehicle should be operated in accordance with the most efficient usage of energy.
Additionally, a hybrid electric vehicle (HEV) encounters many operational states which affect the performance and or efficiency of the vehicle""s operation.
Moreover, and as driving conditions vary, these operational states also vary.
For example, and during typical driving and/or operating conditions, the vehicle""s battery system will lose a state-of-charge (SOC) in any one of the following instances: providing tractive energy to the vehicles drive train for either vehicle launch or maintaining speed in a pure electric vehicle (EV) mode; supplying energy to the vehicles climate control system, this is even more apparent when the ICE is not running; providing a synchronizing or active damping energy to a motor/generator system for synchronizing the drive train coupled to the vehicle""s ICE; and providing operational energy for the vehicle""s electrical accessories.
Of the aforementioned states only the first two (providing tractive energy and supplying energy to the climate control system) are controllable for state of charge (SOC) management.
On the other hand, the vehicle""s batteries or battery system gains a state of charge (SOC) from the following sources: regenerative mechanical energy generated while the vehicle is braking or coasting down, this is known as xe2x80x9cregenerative brakingxe2x80x9d; and electrical energy generated by a generator coupled to the vehicle""s engine, that applies mechanical energy.
Of the aforementioned regenerative states only the charge generated by the engine is fully controllable, whereas the charge generated through regenerative braking can only be controlled by reducing the energy flowing into the batteries.
An object of the present invention is to provide a hybrid vehicle having a parallel propulsion system wherein the state of charge (SOC) is maintained at or near its nominal value by using the controllable quantities, during discharging and/or charging.
In an exemplary embodiment of the present invention a controller system configures the propulsion system of a hybrid vehicle to provide the most energy efficient means for meeting requested demands.
In another exemplary embodiment of the present invention a system configures the propulsion system of a hybrid vehicle to provide the lowest amount of emissions while at the same time meeting the requested driver demands.